A method allocates uplink radio resources in a reduced transmission time interval (RTTI) configuration, in particular for enhanced general packet radio service (EGPRS) in global system for mobile communications (GSM)/enhanced data rates for global evolution (EDGE) radio access network (GERAN).
In some systems in which transmission and reception cannot occur at the same time. In order to allow timeslots having the same timeslot number to be used for both transmission and reception, conventionally, in frames of eight timeslots, the downlink and uplink timeslots having the same timeslot numbers are shifted by three timeslot periods from one another.
As, typically, several mobile devices or users share the same uplink timeslots, they need to know which of them is permitted to use a timeslot at any particular time. The network provides a notification, in the downlink timeslots, of which mobile device can transmit on each uplink timeslot. The network uses an uplink status flag (USF) in the downlink which has a value corresponding to a unique number given to the mobile, to indicate which mobile device can use the next uplink timeslot. This process of indicating which device can use an uplink timeslot is referred to as “allocation”, which is different from the “assignment” of timeslots that occurs, typically, during session set-up. Assignment of timeslots refers to granting of radio resources on a semi-static basis, whereas allocation of timeslots refers to the dynamically changing permission to use those resources that have been assigned to a user and are shared with other users. In this case radio resources are physical data channels (PDCHs), i.e. timeslots, provided by the network to the mobile station.
In EGPRS, two uplink allocation methods exist, dynamic allocation (DA) and extended dynamic allocation (EDA). In dynamic allocation, if the mobile device sees its value of the USF in a downlink timeslot, it is then permitted to transmit in the uplink timeslot with the same timeslot number. In extended dynamic allocation, if the mobile device sees its value of the USF in a downlink timeslot, it is then permitted to transmit in the uplink timeslot with the same timeslot number and all the assigned uplink timeslots with a higher timeslot number. The USF is received in one radio block period and the transmission takes place in the next radio block period.
Initially, in EGPRS, the number of timeslots assigned in uplink and downlink had to be such that their sum does not exceed the parameter “Sum”, which is a characteristic of the multislot class of the mobile station (MS). The multislot class indicates the capability of the mobile station and says how many timeslots the mobile can receive and transmit on in a certain period, typically a single time division multiple access (TDMA) frame. In later versions of EGPRS, changes have been made to the way that extended dynamic allocation works [GP-062076, “Flexible timeslot assignment”, Siemens Networks, GERAN#32, Sophia Antipolis (France), 13-17 Nov. 2006]. In particular, the flexibility of the allowed multislot configurations has been increased by allowing the possibility that the parameter “Sum” of the MS multislot class applies not to the mobile station's timeslot assignment but to the mobile station's timeslot allocation (as described in subclause 6.4.2.2 of 3GPP TS 45.002). In other words, during the session set-up phase, more than “Sum” UL+DL timeslots can be assigned to the mobile station, whilst still respecting the constraints on reception and transmission for the mobile station's multislot class, with the additional constraint that “Sum” needs to be respected only on a dynamic basis, i.e. within every TDMA frame.
This enhancement, referred to as flexible timeslot assignment (FTA), has been endorsed by GERAN, but for use only with extended dynamic allocation. [GP-062382, “CR 45.002-0112 rev 1 Flexible timeslot assignment (Rel-7)”, Siemens Networks, GERAN#32, Sophia Antipolis (France), 13-17 Nov. 2006]. It could be that “Sum” is equal to 5, i.e. the sum of the downlink and uplink timeslots is up to 5. Without flexible timeslot assignment, there may be, for example, 1 downlink plus 4 uplink timeslots assigned; or 2 downlink plus 3 uplink timeslots assigned. With flexible timeslot assignment, 4 uplink and 4 downlink timeslots can assigned, but the allocations must not exceed a maximum of 5 timeslots in total.
In EGPRS, FTA is only used with EDA, which is acceptable for basic transmission time interval (BTTI) configurations. However, there are also reduced transmission time interval (RTTI) configurations which have been defined in GERAN [GP-062483, “CR 43.064-0044 rev 5 Introduction of Reduced TTI”, Ericsson, GERAN#32, Sophia Antipolis (France), 13-17 Nov. 2006]. Conventionally, one radio block has been sent on only one timeslot in four TDMA frame periods, but in RTTI configurations one radio block is sent on two timeslots in two TDMA frame periods. The same block is transmitted more quickly by taking more physical resources. One possible application for this is voice over internet protocol (VoIP), where voice data is sent as packets which must appear instantaneous to the user. Using RTTI reduces the latency to give this impression. Another possibility is to send the whole block on four timeslots in one TDMA frame period, although this is not in use currently.
Some rules need to be set for the allocation of uplink radio blocks for RTTI configurations. There are a number of issues regarding the allocation of uplink radio blocks for RTTI temporary block flows (TBFs), for example VoIP.